1. Field of the Invention
Embodiments of the invention relate to the field of semiconductor device fabrication. More particularly, the present invention relates to a wafer handling apparatus used to transport wafer materials among devices.
2. Discussion of Related Art
Silicon wafers are used in semiconductor and solar cell fabrication. The wafers are subjected to a multi-step manufacturing process that may involve a plurality of machines and a plurality of stations. Thus, the wafers need to be transported from one machine/station to another machine/station one or more times.
The transport of the wafers typically employs apparatuses called end effectors. A typical end effector may be hand-like in appearance where a base unit may attach to a plurality of finger-like extensions. On each of the finger-like extensions, a plurality of wafers may be seated atop wafer pads at spaced apart intervals. The end result may be a matrix of wafers supported by the plurality of end effector fingers. The end effector may typically be moved linearly (e.g., forward and backward) as well as rotationally all in the same plane (e.g., x-y axis). The end effector may also be moved in a third direction along a z-axis to provide a full range of motion.
There are several styles of wafer interface features used in semiconductor wafer handling equipment. Sometimes silicone pads are used to isolate the silicon wafer from the metallic robot end effector fingers. Sometimes semiconductor wafers sit on hard slippery pads affixed at periodic intervals along the end effector fingers. The hard slippery pads are typically made of a polyetheretherketone (PEEK) plastic which is a high performance thermoplastic material comprised of a polymer that is semi-crystalline. PEEK plastic is advantageous in that it retains its mechanical properties at extremely high temperatures, is weldable, machinable, and can be bonded with epoxies cyanoacrylates, polyurethanes, or silicones. PEEK also does not outgas under vacuum and is a generally acceptable material allowed to touch semiconductor wafers.
There are several styles of wafer interface features used in wafer handling equipment. Sometimes silicone pads are used in wafer handling equipment to separate the silicon wafer from a typically metallic robot end effector finger. If the silicon wafer were contacted by a metallic end effector finger, the wafer could be contaminated with the parent metal of the end effector finger. A recent development in wafer handling includes a typically hard polymer pad (e.g., PEEK) having a lip formed thereon. The wafer sits on the pad and is pushed against the lip as the end effector apparatus is accelerated or decelerated into position. The lip on the pad is used to align the wafer with respect to the end effector and ensure proper wafer alignment when the wafer is delivered to a process station. If such a hard polymer pad supporting a wafer along an end effector finger is rotated too rapidly, the wafer can slip sideways off the end effector apparatus. Wafers on hard polymer pads can also slip during linear motion events when the end effector vibrates or the robot control system is not tuned properly causing the end effector fingers to also vibrate.